By: Audella Eid

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Constructed Wetlands for Wastewater treatment
By Audella Eid Advisor Dr. R. Zurayk
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What are constructed wetlands ?

• CW are complex, integrated systems in which
  water, plants, microorganisms, and the
  environment all interact to improve water
  quality.
• CW have been used in Europe since the 1960s.

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Usage of CW

• Municipal wastewater treatment
• Acid mine drainage
• Agricultural point and non-point discharges
• Storm water treatment

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Important Characteristics of CW

• Inexpensive
• Low-maintenance
• Easy operation
• High removal efficiencies under various temp, pH,
  hydraulic and biological loading rates.

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Types of CW

• Free-water surface (FWS) wetland

• Subsurface Flow (SF) wetland

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Free-water surface (FWS)

• Are earthen basins or channels filled with
  shallow water and emergent vegetation.
• Wastewater is exposed to the atmosphere.
• Recommended for lower strength wastewater,
  stormwater treatment or where nitrogen removal is
  required.

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Subsurface Flow wetland (SF)

• Is composed of a cement cell filled with a
  porous media such as rock or gravel.
• Wastewater percolated through a porous medium
  that supports the root system of the vegetation.
• Water flows below the porous surface and is not
  exposed to the environment.

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SF ( contd)

• Recommended for residential homes, schools and
  other areas where the exposed wastewater
  treatment site may not be suitable.
• Decrease chance of exposure, odor and insect
  vectors.

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Treatment of wastewater

• CW treat wastewater using the following
  processes
• Filtration
• Sedimentation
• Physical or chemical immobilization
• Chemical and biological decomposition
• Absorption and assimilation of excess nutrient
  by plants

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• In each of the two systems march plants aid in
• the treatment of water by improving conditions
  for the microorganisms living in the cells.
• and by acting as a filter to absorb some trace
  metals.

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How do they operate?

• Plants and microorganisms play a key function in
  the cleaning of the wastewater.
• Plant roots transpire oxygen and thus aerate the
  water.

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How do they operate?(contd1 )

• Large populations of aerobic and anaerobic
  bacteria grow within the rhizosphere (which is
  the small area surrounding the root zone).
• These microbes are the primary source of
  treatment, breaking down the complex dissolved
  organic and nutrient pollutants into simpler
  forms that the plants use as food.

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How do they operate?(contd2)

• Aerobic conditions in the root zones of the
  plants also facilitates growth of large
  microorganisms (protozoa) that are essential to
  the removal of bacteria, such as fecal coliforms.
• The most common plant used for subsurface flow is
  the common reed (Phragmites australis).

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The Gharzouz experience
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The Gharzouz Reed Bed

• The choice of using a constructed wetland for
  wastewater treatment was based on
• environmental feasibility
• social acceptance
• economic feasibility
• previous removal efficiencies

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Environmental feasibility

• The place is relatively isolated with a lot of
  land around it and a large area for the wetland
  construction.
• The possibility of using the effluent in
  irrigating of the olive and other trees that is
  present in the area.

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Social acceptance

• The community is a relatively very small
  ranging from 15 to 50 people at different times.
• They accepted the implication of this technique

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Economic feasibility

• The budget available for wastewater treatment is
  not very high.
• The difference in costs between construction of
  a wetland and using a mechanical method.

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Previous removal efficiency

• Previous studies that showed high reduction
  rates of BOD , SS and nitrates.
• The previous pilot tests that were done on this
  system (in AUB and other places in Lebanon) and
  proved to be efficient in reducing BOD and other
  measures.

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Characteristics of the gravel bed
t VPorosity of the gravel bed (assumed to be
35)/Q BOD loading rate Co(avg)Q /A
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MONITORING
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Methodology

• 15 samples of wastewater were collected from
  June 1999 till March 2000.
• Analysis was carried out using standard method
  for COD, BOD, TSS, TDS, Nitrates, Ammonia,
  Phosphates, Sulfates, conductivity, pH, Fecal
  coliforms, Total Coliforms

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RESULTS AND DISCUSSION
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Comparison of the percent removal rates between
previous studies and the current one
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Comparison between typical performance data and
Gharzouz data
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LIMITATIONS AND CONCERNS
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Limitations

• Large land area requirements.
• Lack of a consensus on design specifications.
• Long term effectiveness is not known. Wetland
  aging may contribute to a decrease in contaminant
  removal rates over time.

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Limitations (Contd)

• When metals are key contaminant, CW do not
  destroy them but only restrict their mobility.
• Performance may be more variable and less
  predictable than other treatment methods.

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COSTS
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COSTS
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CONCLUSION
The Gharzouz experience indicates that CW may be
an appropriate, low-cost alternative for small
rural communities!
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THANK YOU